Shell script fails to execute repeatedly automatically

Before we pass terminal And linux When the system interacts , Some commands are often used . However, some commands are time-consuming , For example, I want to give an example of the synchronous download command . We can't wait for hours by the computer to wait for the command to finish and then carry out some operations . What's more hateful , The command may fail to execute , At this time, it needs to be re executed . We need a result that can receive the last command , Then do the corresponding treatment according to the results , For example, restart the command and so on .
The code is as follows

#！/bin/bash
repo sync
echo "======sync starting======"
while(($? == 1))
do
sleep 3
du -sh >> abc.txt
echo "======sync failed,re sync starting====="
repo sync
done

This code begins #! /bin/bash The interpreter that executes for the specified script , Which one shell The interpreter executes this shell Script .
repo sync For downloading scripts , If he makes a mistake , that $? Just read 1, So enter a cycle ,
du -sh >> abc.txt This code is to write the total capacity data of the current folder to abc.txt This document should be established in advance .
And then execute it again repo sync Until he ends the order normally .